This invention relates to a switching type liquid-in vibration isolating device used to support a vibration generating source such as power unit of automobile for the purpose of vibration isolation.
A liquid-in vibration isolator has heretofore been used as a mount supporting a vibration generating source such as vehicle engine so as not to transmit its vibration to a vehicle body.
As one of the liquid-in vibration isolators, a switching type liquid-in vibration isolating device, in which vibration isolating characteristics is changed over according to two kinds of vibration with different frequency range such as shake and idle vibration, has been suggested.
For example, in an official gazette JP-A-8-270718, a switching type liquid-in vibration isolating device as shown in FIG. 5 is disclosed.
This conventional vibration isolating device is equipped with a first fitting (101), a second fitting (102) in the form of a bottomed cylindrical body with its bottom wall located at a given distance in the direction of an axis from the first fitting (101), and a vibration isolating substrate (103) made of a rubber elastomer interposed between the first fitting (101) and the second fitting (102) to connect both fittings. Within a hollow space between the vibrating isolating substrate (103) and the second fitting (102), a partition member (104), a first diaphragm (105) and a second diaphragm (106) are disposed serially in the direction of an axis, a main liquid chamber (107) is formed between the vibration isolating substrate (103) and the partition member (104), and a sub-liquid chamber (108) is formed between the partition member (104) and the first diaphragm (105). Further, a equilibrium chamber (109) is formed between the first diaphragm (105) and the second diaphragm (106), and a switching chamber (110), capable of selectively introducing the atmospheric pressure and negative pressure, is formed between the second diaphragm (106) and the second fitting (102). An outside orifice (113) and an inside orifice (114) located further radially inwardly from the outside orifice (113) are disposed on the partition member (104) to interconnect the main liquid chamber (107) and the sub-liquid chamber (108). A coil spring (127) is disposed in the switching chamber (110) to force or push-in the first diaphragm (105) via the second diaphragm (106) against the partition member (104). A pipe (128) for introducing the atmospheric and negative pressure into the switching chamber (110) is pierced through the bottom wall of the second fitting (102). When the atmospheric pressure is brought through this pipe (128) into the switching chamber (110), the first diaphragm (105) is forced on the partition member (104) by the coil spring (127) to impede liquid flow between the inside orifice (114) and the sub-liquid chamber (108). However, since the first diaphragm (105) moves against an energizing force by the coil spring (127) when negative pressure is brought from the pipe (128) into the switching chamber (110), the first diaphragm (105) separates from the partition member (104) to make the inside orifice (114) connect to the sub-liquid chamber (108). Thus, as for the vibration isolating device, the inside orifice (114) can be opened and/or closed by selectively changing over between the atmospheric and negative pressure in the switching chamber (110), so that the orifice can be used selectively according to two kinds of vibration of different frequency range, respectively.
As for this known vibration isolating device, the pipe (128) for introducing the atmospheric and negative pressure into the switching chamber (110) is fitted and secured by a welding means and the like under a condition of projecting from the bottom surface of the second fitting (102). With the pipe (128) thus being projected, when the vibrating isolating device is placed on a work or transport stand before placing the vibration isolating device on board of the vehicle, the pipe (128) will support deadweight of the vibration isolating device, with the result that the pipe (128) may be disconnected. This pipe (128) is fixed to the second fitting (102) so that it is difficult to be pulled out of the second fitting (102) by taking into account after placing on board of the vehicle. That is, the pipe (128) is strong against a load in the direction of pulling and weak against a load in the direction of pushing in the switching chamber (110), therefore, before placing the vibration isolating device on board of the vehicle, a problem of disconnection of the pipe (128) is prone to occur.
In view of the descriptions above, this invention provides a liquid-in vibration isolating device capable of opening/closing an inside orifice out of two inside and outside orifices by selectively changing over between the atmospheric and negative pressure in a switching chamber so as to selectively use orifices corresponding to two kinds of vibrations with different frequency range such as shake and idle vibration, and has an object of preventing a pipe for introducing the atmospheric and negative pressure into the switching chamber from disconnecting.
The switching type liquid-in vibration isolating device is equipped with a first fitting, a second fitting in the form of a bottomed cylindrical body with its bottom wall located at a given distance in the direction of an axis from the first fitting, a vibration isolating substrate made of a rubber elastomer interposed between the first and second fittings to connect both fittings, a partition member, a first and second diaphragm disposed serially in the direction of an axis within a hollow space between the vibration isolating substrate and the second fitting, a first liquid chamber formed between the vibration isolating substrate and the partition member, a second liquid chamber formed between the partition member and the first diaphragm, an outside orifice interconnecting between the first and second liquid chambers disposed on the partition member, an inside orifice located further radially inwardly from the outside orifice, a equilibrium chamber formed between the first diaphragm and the second diaphragm, a switching chamber formed between the second diaphragm and the second fitting capable of selectively introducing the atmospheric pressure and negative pressure, and energizing means forcing or pushing-in the first diaphragm against the partition member, and the first diaphragm is forced or pushed-in against the partition member by the energizing means to close the inside orifice when introducing the atmospheric pressure into the switching chamber, and further the first diaphragm is separated from the partition member against the energizing force exerted by the energizing means to open the inside orifice when introducing the negative pressure into the switching chamber, a part of the bottom wall of the second fitting being depressed toward the switching side, a pipe for introducing the atmospheric and negative pressure into the switching chamber being pierced into the top of the depressed portion and received in the depressed portion, and a plurality of convex portions outwardly projectively being provided on the bottom wall around the depressed portion.
Thus, it is possible that the pipe is not projected downwardly from the bottom surface of the second fitting by providing the depressed portion on the bottom wall of the second fitting and receiving the pipe, for introducing the pressure, inside the depressed portion. Therefore, when the vibrating isolating device is placed on a work or transport stand before placing the vibration isolating device on board of the vehicle, the pipe will no longer support deadweight of the vibration isolating device, capable of securely preventing the pipe from being disconnected.
Although it is desirable that the introducing pipe is completely received in the depressed portion, there are some cases where the pipe must be projected slightly downward from the inside of the depressed portion. That is, the pipe is required to be projected outwardly from the switching chamber to some extent to connect the piping from the switching valves when placing the device on board of the vehicle, the height of the depressed portion is limited by the dimensions of the switching chamber in the direction of an axis, etc. According to the vibration isolating device of the invention, even in such circumstances, it is possible to avoid the pipe from interfering with the placing surface of such as work or transport stands by means of the convex portions projectively provided outwardly around the depressed portion.
As for the vibration isolating device of the invention, a press-fitting area of the second diaphragm is secured at the circumferential edge portion of the bottom wall of the second fitting, and the second diaphragm may be press-fitted from the upper portion on the opening side of the second fitting and fixed in the press-fitted area. Thereby, it is not necessary to caulk and secure the second diaphragm in conjunction with the second fitting.
The energizing means in the vibration isolating device of the invention is a coil spring interposed between the bottom wall of the second fitting and the second diaphragm in the switching chamber, for forcing the first diaphragm via the second diaphragm against the partition member, a receiving surface of the coil spring may be secured on the bottom wall around the depressed portion of the second fitting, and the coil spring may be disposed on the receiving surface in such a manner as to surround the depressed portion. Thus, it is possible to position the lower extremity of the coil spring at the outer circumference of the depressed portion and prevent the coil spring from getting out of position on the bottom wall of the second fitting, by securing the receiving surface of the coil spring around the depressed portion for receiving the pipe and disposing the coil spring so as to surround the depressed portion.
As for the vibration isolating device of the invention, a stopper rubber may be provided on the second diaphragm, and an abutting surface of the stopper rubber portion may also be secured on the bottom wall around the depressed portion of the second fitting. Thus, undesired downward displacement of the second diaphragm can be limited when introducing the negative pressure into the switching chamber.
In this case, the convex portion can be provided on the bottom wall portion which corresponds to the abutting surface of the stopper rubber portion. Since it is not necessary to secure the abutting surface on the stopper rubber portion all over in the circumferential direction, the convex portion can be provided especially for such portion without impairing the performance.
With regard to the vibration isolating device of the invention, the depressed portion may be provided at the center portion of the bottom wall of the second fitting and the receiving surface of the coil spring may be secured around the depressed portion, and the abutting surface of the stopper rubber portion may also be secured between the receiving surface and the press-fitting area of the second diaphragm.